E. Dealba et al., TURN RESIDUE SEQUENCE DETERMINES BETA-HAIRPIN CONFORMATION IN DESIGNED PEPTIDES, Journal of the American Chemical Society, 119(1), 1997, pp. 175-183
A series of linear peptides designed to fold into different beta-hairp
in conformations in aqueous solution has been studied by H-1 NMR with
the aim of understanding the role played by the turn residue sequence
in defining beta-hairpin structure. The designed peptides differ only
in the amino acid sequence of the putative turn region and have identi
cal strand residues. Our results clearly demonstrate that the turn res
idue sequence determines the turn conformation and, thereby, other fea
tures of the beta-hairpin conformation, such as the pattern of interst
rand residue pairing and the type of hydrogen-bonding register between
beta-strand backbone atoms. Furthermore, two key structural factors r
esponsible for the stability of different types of turns were identifi
ed. Thus, a side-chain-side-chain interaction between Asn at position
i and Thr at position i + 4 stabilizes five-residue turns, whereas a f
our-residue turn is stabilized when the first residue of the turn has
high tendency to populate the alpha(R) region of the Ramachandran map.
Our results highlight the relevance of turn structures in the early e
vents of protein folding.